1. Field of the Invention
This invention relates to a chain stitch sewing machine, more particularly to a chain stitch sewing machine, which includes a needle-thread pushing member that moves between a presser foot and stitching needles along a curved path.
2. Description of the Related Art
Referring to FIG. 1, a conventional chain stitch sewing machine 1 is shown to include a machine bed 10, a machine frame 11 fixed relative to the machine bed 10, a presser foot 12, a needle seat 13, a thread pushing device 2 and a thread cutting device 6. The presser foot 12 is adapted to press a fabric 14 on a top surface of the machine bed 10. The needle seat 13 is mounted vertically and movably on the machine bed 10, and carries a row of three vertical stitching needles 131, 131', 131" thereon. The middle needle 131' is shorter than the front needle 131, and is longer than the rear needle 131". As such, the lower end of the middle needle 131' is located above that of the front needle 131, and below that of the rear needle 131". The thread pushing device 2 includes two bolts 21, a mounting member 22, a power source 23, a swing arm 24, an upper rotating element 25, a lower rotating element 26, a connecting rod 27 and a needle-thread pushing member 28. The bolts 21 extend respectively through two side slots 221 in the mounting body 22, thereby locking the mounting body 22 on the machine frame 11. The swing arm 24 is mounted rotatably on the mounting body 22, and can be swung by the power source 23. The upper and lower rotating elements 25, 26 are journalled respectively on the mounting body 22 and the swing arm 26. Each of the rotating elements 25, 26 can rotate about a horizontal axis. The connecting rod 27 is fixed to the rotating elements 25, 26. When the power source 23 is driven, the swing arm 24 activates the connecting rod 27 to move the needle-thread pushing member 28 forward from the position shown by the solid lines to that shown by the phantom lines, thereby moving the same between the presser foot 12 and the needles 131, 131', 131" forward along a generally horizontal path. The aforementioned conventional sewing machine 1 suffers from the following drawbacks:
(1) When the thickness of the fabric 14 or the lengths of the needles 131, 131', 131" are changed, it is necessary to adjust the positions of the bolts 21 relative to the slide slots 221 in the mounting body 22. This adjustment is relatively difficult to conduct. PA1 (2) When the needle-thread pushing member 28 is moved to the generally horizontal position shown by the phantom lines, it is spaced apart from the rear needle 131" by a relatively large distance. As such, it is difficult for the pushing member 28 to push a needle thread, which is suspended from the needle 131", away from the presser foot 12 just before the presser foot 12 moves downward toward the fabric 14. As a result, the suspended needle threads may be clamped between the presser foot 12 and the fabric 14. Furthermore, in a case where the pushing member 28 is adjusted to an excessively low position, it may strike the presser foot 12 during forward movement thereof.